procedure to find port by ip arp mac

Assumptions:
You have an IP address and want to find out what switch port it is on.
There is a core switch with edge switches and Cisco CDP is running.
Example: IP address is 10.1.1.69
- find the MAC address of this IP
open ssh console to core switch and run “sh arp”
coreswitch#sh arp | inc 10.1.1.69
Internet 10.1.7.69 0 0007.1234.cd43 ARPA Vlan5
- find port from MAC address
coreswitch#sh mac-address-table dynamic | inc 0007.1234.cd43
* 5 0007.1234.cd43 dynamic Yes 5 Gi7/12
- find edge switch for port
coreswitch#sh cdp nei gi7/12
Capability Codes: R – Router, T – Trans Bridge, B – Source Route Bridge
S – Switch, H – Host, I – IGMP, r – Repeater, P – Phone
Device ID Local Intrfce Holdtme Capability Platform Port ID
edgeswitch.company.net
Gig 7/12 176 S I WS-C3560G-Gig 0/49
- open ssh console to edge switch and run “sh arp” repeat process

How to use NMAP to count the number of hosts on a given subnet.

#!/bin/bash
echo 4192 > /proc/sys/net/ipv4/neigh/default/gc_thresh3
nmap -sP -PI $1 -n –max_rtt_timeout 5000 –initial_rtt_timeout 5000 | tail -1 | cut -f 2 -d “(” | cut -f 1 -d ” ” 2> /dev/null

(Thanks to Gabriel for this one!)